Monolithic ink jet nozzle formed from an oxide and nitride composition

ABSTRACT

An ink jet nozzle. The ink jet nozzle includes a substrate having an upper surface in which an ink energizing element is attached to the upper surface of the substrate. The ink jet nozzle further includes an oxide-nitride or oxide-carbide composite orifice layer. The oxide-nitride composite orifice layer includes a lower surface conformally connected to the upper surface of the substrate, and an exterior surface facing away from the substrate. The oxide-nitride composite orifice layer defines a firing chamber. The firing chamber opens through a nozzle aperture in the exterior surface, and extends downward with a negative slope through the oxide-nitride orifice layer to expose the ink energizing element.

FIELD OF INVENTION

This invention relates generally to an ink jet print nozzle. Inparticular, it relates to an ink jet print nozzle in which inner wallsof the ink jet print nozzle are formed from an oxide-nitride oroxide-carbide composition.

BACKGROUND

Ink jet printing mechanisms use pens that shoot droplets of ink onto aprintable surface to generate an image. Ink jet printing mechanisms maybe used in a wide variety of applications, including computer printers,plotters, copiers, and facsimile machines. For convenience, the conceptsof the invention are discussed in the context of a printer.

An ink jet printer typically includes a print head having a multitude ofindependently addressable firing units. Each firing unit includes an inkchamber connected to a common ink source, and to an ink jet printnozzle. A transducer within each ink chamber provides the impetus forexpelling ink droplets through the associated ink jet print nozzle.Typically, the transducer is a firing resistor which heats the ink untilthe ink droplets are expelled through the ink jet print nozzle.

Generally, a substrate supports the firing resistors. An orifice layerwhich includes the ink jet nozzles is attached to the substrate so thateach ink jet nozzle corresponds with an associated firing resistor andforms an ink chamber.

To obtain a high resolution printed output, it is desirable to maximizethe density of the firing units, requiring miniaturization of the printhead components. The substrate that supports the firing resistors andthe orifice layer that provides the ink jet nozzle above each resistorare subject to small dimensional variations that can accumulate andlimit miniaturization.

Monolithic print heads have been developed through print headmanufacturing processes which use photo imaging techniques similar tothose used in semiconductor manufacturing. The components areconstructed on a flat wafer by selectively adding and subtracting layersof various materials. Using photo-imaging techniques, dimensionalvariations are limited. Further variations do not accumulate becauseeach layer is registered to an original reference on the wafer.

Existing monolithic print heads are complex to manufacture. Further, theink jet nozzles are formed from either a polymer or metal material.Polymer and metal materials offer limited performance because thesurfaces of these materials can be rough, and because these materialsreact corrosively with the ink. It is important that the surface of theink jet nozzle be smooth so as to not interrupt the flow of ink throughthe ink jet nozzles. Further, corrosive reactions to the ink cause theink jet nozzles to break down and deteriorate.

It is desirable to have an ink jet nozzle in which the surface of theink jet nozzle is formed from a material which is smoother thanpresently existing materials. Further, the material would not react toink which flows through the ink jet nozzle thereby increasing the usefullife of the inkjet nozzle.

SUMMARY OF THE INVENTION

The present invention provides a monolithic ink jet nozzle which isformed from an oxide-nitride or oxide carbide composition. Thesecompositions provide an ink jet nozzle which includes a smootherre-entrance surface than presently existing ink jet nozzles. Further,the compositions do not corrosively react to ink passing through the inkjet nozzle. Therefore, the ink jet nozzle is useful for a longer periodof time than presently existing ink jet nozzles.

A first embodiment of the invention includes an ink jet nozzle. The inkjet nozzle includes a substrate having an upper surface in which an inkenergizing element is attached to the upper surface of the substrate.The ink jet nozzle further includes an oxide-nitride or oxide-carbidecomposite orifice layer. The composite orifice layer includes a lowersurface conformally connected to the upper surface of the substrate, andan exterior surface facing away from the substrate. The compositeorifice layer defines a firing chamber. The firing chamber opens througha nozzle aperture in the exterior surface, and extends downward with anegative slope through the composite orifice layer to expose the inkenergizing element.

Another embodiment of the invention includes a method of forming an inkjet nozzle over an ink energizing element on an upper surface of asubstrate. The method includes the following steps. First, a positivesloped sacrificial oxide bump is created on the surface. Next, a nitrideor carbide composite layer and an oxide layer are deposited over thesurface and the sacrificial bump. The oxide and composite layers arepolished forming an orfice layer. An opening in the orifice layer iscreated over the sacrificial oxide bump. Finally, the sacrificial oxidebump is removed yielding an ink jet nozzle.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an ink jet pen having a print head whichincludes ink jet nozzles according to the invention.

FIG. 2 is a cross-sectional view of an embodiment of the invention.

FIG. 3 is a perspective view of the embodiment of the invention shown inFIG. 2.

FIGS. 4A-4H show a series of steps in the formation of an embodiment ofthe invention.

FIGS. 5A, 5B show alternative processing steps to the processing stepsshown in FIGS. 4A-4C.

DETAILED DESCRIPTION

As shown in the drawings for purposes of illustration, the invention isembodied in a monolithic ink jet nozzle. The ink jet nozzle is formedfrom an oxide-nitride or oxide carbide composition. The compositionprovides an ink jet nozzle which is smoother than presently used polymerink jet nozzles. Further, the composition does not react to ink passingthrough the ink jet nozzle. Therefore, the ink jet nozzle lasts longerthan presently existing ink jet nozzles.

FIG. 1 is a perspective view of an ink jet pen 10 having a print head 12which includes ink jet nozzles 18 according to the invention. The inkjet pen 10 also includes a lower portion 14 containing an ink reservoirthat supplies ink to the print head 12.

FIG. 2 is a cross-sectional view of an embodiment of the invention. Thisembodiment includes an ink jet nozzle 18. The ink jet nozzle 18 isformed by a fructoconical firing chamber 36 of an orifice layer 30attached to a silicon substrate 20. The substrate 20 includes a topsurface 22 that is typically coated with a passivation layer 24. A thinfilm resistor 26 is typically formed over the top surface 22. The topsurface 22 of the substrate forms a bottom section of the ink jet nozzle18 which receives ink. The orifice layer 30 has a lower surface 32 thatconformally rests above the top surface 22.

The ink jet nozzle 18 include walls 41 which are negatively sloped froma smaller circular external orifice 16 to a larger circular baseperiphery 40. The larger circular base periphery 40 is centered aroundthe thin film resistor 26. The ink jet nozzle 18 is aligned on an axisof the thin film resistor 26.

The passivation layer 24 defines several ink supply vias 42 dedicated tothe ink jet nozzle 18. The vias 42 are entirely encircled by the lowerperiphery 40 of the ink jet nozzle 18.

The walls 41 of the ink jet nozzle 18 are formed from a oxide-nitride oroxide-carbide material. The oxide-nitride or oxide-carbide materialallows the walls 41 to be smoother than previously possible. Polymerwalls, for example, are rougher. Rough walls impede the flow of inkflowing through the ink jet nozzle 18. The smooth walls 41 of the inkjet nozzle 18 of the invention do not impede the flow of ink passingthrough the fructoconical firing chamber 36 as much as rough polymer orrough metal walls.

The oxide-nitride or oxide-carbide walls 41 of the ink jet nozzle of theinvention do not react to ink passing though the fructoconical firingchamber 36. Prior art ink jet nozzles are generally formed frommaterials which react to ink which makes physical contact with thesurface of the nozzles. The reactions reduce the useable life time ofthe ink jet nozzle. That is, the material of the ink jet nozzle beginsto break down, thereby reducing the performance of the ink jet nozzle.

The substrate 20 includes a tapered trench 44 which provides a path forink to flow between the reservoir 14 and the ink jet nozzle 18.

FIG. 3 is a perspective view of an embodiment of the invention. Aconductor 46 provides a conductive path for current flowing through thethin film resistor 26. The thin film resistor 26 is a firing resistorwhich heats the ink until the ink droplets are expelled through the inkjet print nozzle 18.

FIGS. 4A-4H show a series of processing steps in the formation of anembodiment of the invention. First, a structure as shown in FIG. 4A isformed which includes a substrate 50, a first silicon-oxide (SiO₂) layer52 and tantalum (Ta) layer 54. A second silicon-oxide layer 56 isdeposited over the Ta layer 54. A poly-silicon layer 58 is depositedover the second-silicon oxide layer 56. Finally, a photo-resist layer 60is deposited over the poly-silicon layer 58. The photo-resist layer 60is patterned so that an island 62 of photo-resist is located where anink jet nozzle is to be formed over the substrate 50. The photo-resistlayer 60 pattern can be formed by a standard lithography process.

FIG. 4B shows the structure of FIG. 4A in which portions of thepoly-silicon layer 58 and the photo-resist layer 60 have been removedthrough dry etching. Dry etching the poly-silicon layer 60 forms apattern in the poly-silicon layer 58 as determined by the patternoriginally formed in the photo-resist layer 60.

FIG. 4C shows the structure of FIG. 4B in which the second silicon-oxidelayer 56 has been wet oxide isotopically etched. An aperture 64 isformed in the siliconoxide layer as determined by the pattern of thepoly-silicon layer 58. The aperture 64 encircles a sacrificial bump 66.The sacrificial bump 66 is located where the ink jet nozzle is to beformed. The sacrificial bump 66 include positively sloped edges 68 whichdefine the negatively sloped edges of the ink jet nozzle to be formed.

FIG. 4D shows the structure of FIG. 4C in which the poly-silicon layer58 has been etched away, and a silicon-nitride (Si₃ N₄) orsilicon-carbide (SiC) layer 70 has been deposited over the secondsilicon-oxide layer 56.

FIG. 4E shows the structure of FIG. 4D in which a third silicon-oxidelayer 72 has been deposited over the silicon-nitride layer 70.

FIG. 4F shows the structure of FIG. 4E in which the third silicon-oxidelayer 72 has been chemically-mechanically polished (CMP). The thirdsilicon-oxide layer 72 is chemically-mechanically polished down to thesilicon-nitride or silicon-carbide layer 70 forming an orifice layer 74.The orifice layer 74 includes the second silicon-oxide layer 56, thesilicon-nitride or silicon-carbide layer 70, and portions of the thirdsilicon-oxide layer 72.

FIG. 4G shows the structure of FIG. 4F in which a protective layer 75and second photo-resist layer 76 have been deposited over the orificelayer 74. The protective layer 75 and the second photo-resist 76 includean opening 78 aligned with the sacrificial bump 66. A portion of thesilicon-nitride layer 70 which is aligned with the opening 78 is nitridedry etched down to the silicon-oxide layer 56 leaving the sacrificialbump 66 exposed. The protective layer is either a silicon-carbide and asilicon-nitride. Silicon-carbide may be the preferred protective layer75 material because silicon-carbide provides a very hard surface.

FIG. 4H shows the structure of FIG. 4G in which the exposed sacrificialbump 66 and the second photo-resist layer 76 have been removed throughwet oxide etching. Removing the sacrificial bump 66 results in theformation of an ink jet nozzle 80 in the orifice layer 74.

FIGS. 5A, 5B show alternative processing steps to the processing stepsshown in FIGS. 4A, 4B, 4C. First, a structure as shown in FIG. 5A isformed which includes a substrate 50, a first silicon-oxide (SiO₂) layer52 and tantalum (Ta) layer 54. A second silicon-oxide layer 56 isdeposited over the Ta layer 54. Finally, a photo-resist layer 60 isdeposited over the silicon-oxide layer 56. The photo-resist layer 60 ispatterned so that an island 62 of photo-resist is located where an inkjet nozzle is to be formed over the substrate 50. The photo-resist layer60 pattern can be formed by a standard lithography process.

FIG. 5B shows the structure of FIG. 5A in which the second silicon-oxidelayer 56 has been dry etched. An aperture 64 is formed in thesilicon-oxide layer as determined by the pattern of the photo-resistlayer 60. The aperture 64 encircles a sacrificial bump 66. Thesacrificial bump 66 is located where the ink jet nozzle is to be formed.The sacrificial bump 66 include positively sloped edges 68 which definethe negatively sloped edges of the ink jet nozzle to be formed.

Subsequent processing steps to the structure shown in FIG. 5B are thesame as those shown in FIGS. 4D-4H.

Although specific embodiments of the invention have been described andillustrated, the invention is not to be limited to the specific forms orarrangements of parts so described and illustrated. The invention islimited only by the claims.

What is claimed is:
 1. A method of forming an ink jet nozzle over an inkenergizing element on an upper surface of a substrate, the methodcomprising:creating a positive sloped sacrificial oxide bump on thesurface; depositing an etch stop layer and an oxide layer over thesurface and the sacrificial bump; polishing the oxide to the etch stoplayer forming an orifice layer; creating an opening in the orifice layerover the sacrificial oxide bump; and removing the sacrificial oxidebump.
 2. The method of forming an inkjet nozzle as recited in claim 1,wherein the step of creating a sacrificial bump comprises:depositing asilicon-oxide layer over the upper surface of the substrate; depositinga hard mask layer over the silicon-oxide layer; removing a pattern ofthe hard mask layer so that an island of hard mask layer is located overthe ink energizing element; wet oxide isotropic etching thesilicon-oxide forming apertures in the silicon-oxide where the hard masklayer has been removed; and etching the remaining hard mask layer andany residual resist.
 3. The method of forming an ink jet nozzle asrecited in claim 1, wherein the step of creating a sacrificial bumpcomprises:depositing a hard mask layer over the silicon layer; removinga pattern of the hard mask layer so that an island of hard mask layer islocated over the ink energizing element; dry etching the silicon-oxideforming apertures in the silicon-oxide where the hard mask layer hasbeen removed; and etching the remaining hard mask layer and any residualresist.
 4. The method of forming an ink jet nozzle as recited in claim2, wherein the step of removing a pattern of the hard mask layercomprises:depositing a resist layer over the hard mask layer so that anisland of resist is located over the ink energizing element; and dryetching the hard mask layer so that the hard mask layer is removed wherethe resist layer does not exist.
 5. The method of forming an ink jetnozzle as recited in claim 2, wherein the step of depositing a hard masklayer comprises depositing a poly-silicon layer.
 6. The method offorming an ink jet nozzle as recited in claim 1, wherein the step ofdepositing an etch layer comprises depositing a nitride layer.
 7. Themethod of forming an ink jet nozzle as recited in claim 1, wherein thestep of depositing an etch layer comprises depositing a carbide layer.8. The method of forming an ink jet nozzle as recited in claim 1,wherein the step of polishing the oxide to the etch stop layer compriseschemically-mechanically polishing the oxide layer to the etch stoplayer.
 9. The method of forming an ink jet nozzle as recited in claim 1,wherein the step of removing the sacrificial oxide bumpcomprises:forming a hole in the orifice layer exposing the sacrificialoxide bump; and wet etching the sacrificial oxide bump forming the inkjet nozzle.
 10. The method of forming an ink jet nozzle as recited inclaim 9, wherein the step of forming a hole in the orifice layercomprises:depositing a photo-resist pattern over the orifice layer; anddry etching the orifice layer forming a hole where the photo-resist doesnot exist.